Laser decontamination device

ABSTRACT

The laser decontamination device includes: a laser oscillator; a scanning device provided with an XY axis scanner and a Z axis scanner to condense the laser beam emitted from the laser oscillator onto the surface of the contaminated article without the intervention of any compound lens such as an f θ lens so as to optically scan the surface; and a surface shape measuring device to measure the surface shape of the contaminated article, the Z axis scanner being provided with a focus position controlling section to automatically adjust a focus position in accordance with an irradiation position such that a focus of the laser beam comes on the surface of the contaminated article based on a shape data obtained at the surface shape measuring device.

TECHNICAL FIELD

The present invention relates to an improvement on a laserdecontamination device, in details, pertaining to such device allowingthe containers and equipment contaminated by RI (Radioisotopes) innuclear power plants under recovery owing to the nuclear accidents orunder decommissioning, facilities in which such RIs are stored, nuclearreprocessing factories, nuclear fuel storage facilities, acceleratorfacilities and so forth to be decontaminated with efficiency anddecontamination performance to be further enhanced than the conventionalcounterpart.

BACKGROUND ART

Conventionally, such decontamination method by laser is known asirradiating substantially parallel light pulse laser beams of loweraverage power output onto the surface of the objects contaminated by theRIs with such objects linearly or planarly scanned, the device employingwhich method is characterized in that the contaminants deriving fromRIs, which are black and others in color and higher in photoabsorption,are vaporized for removal without doing damage on the base metal and assuch.

However, according to the above method by which the pulse laser beamsare rendered into parallel light, making the condensed area smaller forthe purpose of enhancing the power density (irradiation intensity)unavoidably leads to causing uneven irradiation, so that the same spotshall be irradiated several times. On the other hand, enlarging anirradiation area of one pulse causes the power density to be lowered (inthe order of some MW/cm² or less) so that the irradiated beams result inbeing reflected from the lustrous metallic surface, with the result thatthe RIs advanced deeply into the microscopic cracks on the metallicsurface cannot be removed at all.

Further, conventionally, besides the above-mentioned laserdecontamination, such decontamination employing a sandblast, a sanderand a grinder is carried out, according to which mechanical methods inorder to remove the attached RIs, it is general that a portion of thesurface of the object contaminated by them is scraped off by thethickness ranging from 0.05 mm to 0.1 mm or more

However, according to the above-mentioned mechanical methods, during thegrinding not only the RIs are ready to reenter the surface so as tocause recontamination, but also the grinding device (such as the nozzleof the sandblast) is secondarily contaminated by the grinding particlesof the sandblast, the grinding belt of the sander or grinder or thegrinding disk that are used repeatedly.

Further, providing that the sandblasts and sanders secondarilycontaminated by the grinding particles or belt are exchanged with newones every time the decontaminations are carried out, it makes the costincurred for exchanging such mechanical devices and their parts so bulkythat not only the decontamination cost goes overboard, but also a largevolume of secondary wastes are produced, which is unfavorable in view ofthe cost-saving aspect and the eco-friendly trend.

On the other hand, conventionally, such method is known as the objectscontaminated by the RIs being clipped into the solution containing anoxidant and a reductant so as to make the contaminants solved into thesolution, according to which chemical method it requires a lot ofdisposal cost to dispose with a large volume of ion-exchange resins usedfor separating the RIs from the wasted solution, which resins are burntso as to be reduced in volume and stabilized with concrete and the likefor storage.

Further, in recent years, such technique is proposed as the pulsed laserbeams whose peak output is 10 MW or higher (for instance, refer toDocument 1) being employed, according to which technique it is unable tofocus the laser beams on the surface of the object contaminated by theRIs with precision, so that the power density (irradiation intensity) inthe order of GW/cm² cannot be secured. Moreover, uneven irradiationdensity might happen on the surface of the object with irregularities.

Furthermore, where such high-output pulsed laser beams are employed, itrequires that the thermally induced diffusion and reattachment of theRIs be taken into due account, besides, with the method by which thelaser beams are irradiated with the laser head moved, because there islimit in the scanning velocity for the low-velocity motion even when itmight be automatically scanned, the thermally induced diffusion of theRIs is aggravated in which the portions onto which the beams areirradiated result in being extensively and deeply fused and thermallyaffected. Such method is also known (refer to non-patent literature 1)as fusing the surface of the object by CW (Continuous Wave) laser beamsof high output power and removing the fused portions by a pressurizedgas, which method is also subjected to aggravated thermal effect so asto make the thermally induced diffusion of the RIs further aggravated.

On the other hand, a laser machining device in which a focal length isadjusted with a beam expander in use is also well known (refer to PatentLiterature 2), but with such device, the condensing optical systemincluding compound lenses are disposed posterior to the XY scanner, sothat it often happens that measuring a surface shape with a laser rangefinder fails because the reflected light from the object is under theinfluences of such compound lenses and as such. Further, passing themachining and measuring laser beam through the compound lenses and assuch makes such beam greatly attenuated, so that the available machininglaser beam unavoidably results in being smaller in output power.

CITATION LIST Patent Literature

-   Document 1: Japanese Patent Unexamined Application Publication No.    2004-193267.-   Document 2: Japanese Patent Unexamined Application Publication No.    2010-82663.

Non-Patent Literature

-   ‘Development of Laser Decontamination Technique’ contributed by    Ryuichiro OGAWA et. al to the technical report of Japan Nuclear    Cycle Development Institute, pp. 59-66, Issue No. 15 of June 2002.

SUMMARY OF INVENTION Technical Problem

In view of the above-mentioned problems found in the conventionaltechnology, the present invention is to provide a laser decontaminationdevice allowing the power density high enough to remove inclusively theRIs advanced deeply into the contaminated article to be secured anduneven irradiation density to be prevented even when there areirregularities on the surface of the object to be decontaminated andfurther the thermally induced diffusion and recontamination of RIs to bedone without as well as favorably leading to further equipmental andoperational cost reduction as well as more eco-friendly and efficientdecontamination operation.

Solution to Problem

The means adopted by the inventor to solve the above problems isexplained below with reference to the accompanying drawings.

That is to say, the laser decontamination device according to thepresent invention comprises a CW laser oscillator 1 used for a lightsource of a machining laser beam L₁; a scanning device 2 provided withan XY axis scanner 21 to reflectively and two-dimensionally scan thelaser beam L₁ through two beam reflectors 21 a; and a Z axis scanner 22to adjust a focal distance of the laser beam L₁ through a variable focuslens and a movable lens 22 a, which Z axis scanner 22 is disposed nearerto the light source than the XY axis scanner 21 and which scanningdevice 2 condenses the laser beam L₁ scanned by the XY axis scanner 21and the Z axis scanner 22 on a surface of a contaminated article Twithout an intervention of any compound lens such as an f θ lens(hereinafter, referred to as compound lens); and a surface shapemeasuring device 3 to measure a surface shape of the contaminatedarticle T by an optical means employing a laser range finder 31 and theXY axis scanner 21, in which the Z axis scanner 22 is provided with afocus position controlling section 24 to automatically adjust a focusposition according to an irradiation position such that a focus of thelaser beam L₁ comes on the surface of the contaminated article T basedon a shape data obtained at the surface shape measuring device 3,thereby, allowing the laser beam L₁ to be three-dimensionally scannedover and irradiated onto the surface of the contaminated article T withthe focus position of the beam aligned onto the surface of thecontaminated article T.

Further, as for the laser oscillator 1 and the scanning device 2 asmentioned above, a single mode fiber laser of higher average outputpower allowing the beam to be focused onto a minute spot having 10 μm orsmaller in diameter is adopted for the former while the output of thelaser oscillator 1 is adjusted and the optical system is designed suchthat the laser beam L₁ is irradiated onto the surface of thecontaminated article T with the power density of 1 GW/cm² or higher soas to enhance the thermal spallation, evaporation and sublimation of thecontaminated article T without melting in proportion to the powerdensity up to the second power thereof. This enhances the velocity andefficiency with which the decontamination proceeds. Further, thedecontamination is readily available for stainless steel and so forthhaving surface cracks into which RIs are advanced deeply and unable tobe decontaminated by the conventional laser methods.

Further, with a fiber laser provided with an optical fiber whosediameter is smaller used for the laser oscillator 1, emitting the laserbeam L₁ directly onto the beam reflectors 21 a from the optical fiberallows the reducing optical system in which the diameter of an imagepoint is made smaller than that of an object point to be done without.In other words, there is no need to use the reducing optical system thatcauses the scanning velocity and the scanning aerial velocity to lower.

On the other hand, for the surface shape measuring device 3, a laserrange finder 31 that irradiates a measuring laser beam L₂ onto a targeton the surface of the contaminated article T and finds a distance fromthe phase difference by interference or the time difference between theirradiated light and its scattered light is adopted, which finder isdisposed such that the measuring laser beam L₂ can be scannedsimultaneously with or independently from the machining laser beam L₁with the XY axis scanner 21 to scan the machining laser beam L₁,thereby, allowing the efficiency with which the same is measured toenhance.

Further, as for the disposition of the laser oscillator 1, the scanningdevice 2 and the surface shape measuring device 3 respectively, thelaser oscillator 1 is disposed away from the scanning device 2, in whicha fiber laser having an optical fiber smaller in diameter is adopted forthe laser oscillator 1. Further, the Z axis scanner 22, the dichroicmirror 33 (the mirror that reflects the measuring laser beam L₂ from thelaser range finder 31 towards the XY axis scanner 21 and transmits themachining laser beam L₁ passing through the Z axis scanner 22 and goingtowards the XY axis scanner 21) and the XY axis scanner 21 are disposedin this order between the emitting end of the optical fiber and thelaser window 23.

Then, arranging the scanning velocity of the XY axis scanner 21 with thehigher velocity of 10 m/s or faster and the scanning velocity and thefocused beam size of the XY axis scanner 21 such that the reciprocallyscanned machining laser beam L₁ is irradiated onto an arbitraryirradiation spot on the surface subjected to the irradiation with theduration of nanoseconds permits the contaminated article to benon-thermally spalled, evaporated and sublimed with the influence ofthermal conduction minimized even when the laser beam L₁ is irradiatedwith such a high power density as being 1 GW/cm² or higher, with theresult that the problems with the diffusion and reattachment of the RIscan be overcome.

Further, as for the focus position controlling section 24, in order toefficiently spall, evaporate and sublime the RIs with a higher powerdensity and without uneven irradiation density, it is set such that thesurface of the contaminated article T to be irradiated is adjustivelyplaced within the range of the depth of focus (Rayleigh length) of thelaser beam L₁ or in the vicinity thereof.

On the other hand, to the laser decontamination device arranged asmentioned above, adding a gas jet-spraying device 4 to blow offparticles with an inert gas jet-sprayed in the angular directioncontrary to the scanning direction of the laser beam L₁ onto the surfaceof the contaminated article T onto which the machining laser beam L₁ isbeing irradiated and with the irradiated surface constantly covered withthe inert gas; and a removals collecting device 5 to suction and tocollect the removals containing radioactive substances blown off by thegas jet-spraying device facilitates the collection of the removalscontaining the RIs and prevents even the slightest secondarycontamination.

Further, making the scanning device 2 drivable in a wider area of thesurface of the contaminated article T with the laser oscillator 1carried on a remote-controlled robot R provided with the self-runningmeans and the scanning device 2 mounted onto the arm section A of theremote-controlled robot R permits decontamination to be performedwithout the possibility of any operators being exposed to suchcontaminant, in which sequentially irradiating the laser beams with thearm section remotely controlled allows decontamination to be efficientlyperformed even when a wall surface larger in area is decontaminated.

Advantageous Effects of Invention

The invention brings the following favorable effects.

According to the present invention, making the laser beam converged ontominute regions on the surface of the contaminated article by means ofthe imaging optical system (Z axis scanner) and the focal length of thelaser beam precisely adjustable in accordance with the surface of thecontaminated article by means of the Z axis scanner permits the powerdensity of the laser beam to be increased up to in the order of GW/cm²that is larger almost by three orders of magnitudes than theconventional counterpart, so that inclusively the RIs advanced deeplyinto the contaminated article can be completely spalled, evaporated andsublimated along with the base material.

Further, according to the present invention, the condensing optic systemis disposed nearer to the light source than the XY axis scanner suchthat the measuring laser beam emitted from the laser range finder doesnot pass through such system, with the result that the surface shape ofthe target can be accurately measured. Likewise, not using the numeralpieces of compound lenses permits a laser beam of high output power tobe irradiated onto the object contaminated with the RIs with such beamhardly attenuated or without the apprehension that the lenses comprisingsuch system might be broken.

Moreover, according to the present invention, based on the data (cubicmap) of the surface shape of the contaminated article measured by thesurface shape measuring device, the focus position controlling sectionof the Z axis scanner automatically adjusts the focus of the laser beamaccording to an irradiation position, so that time and labor-savingdecontamination can be performed without uneven irradiation density evenwhen the surface of the contaminated article can be irregular.

Further, arranging the scanning device with the XY axis scanneremploying the beam reflectors (such as galvano-mirrors) and the Z axisscanner employing the movable lens (or a variable focus lens) asdescribed in the present invention allows the scanning velocity of thelaser beam to be further enhanced than when the surface of thecontaminated article is scanned with the laser head moved, which enablesnon-thermal machining to be performed even with the laser beam whosepower density is higher, with the result that the thermally induceddiffusion and reattachment of the RIs can be prevented.

Furthermore, with the CW laser that continuously emits laser beams L₁used for the laser oscillator 1, the focused beam size can be renderedpretty smaller than that of the pulse laser so that not only irradiationdensity can be set higher, but also it allows the three-dimensionalscanning to be performed with precision in accordance with the surfaceshape of the contaminated article. Also in the aspect of the relatedcost, it can be saved further than the pulse laser, the cost of whichdevice per laser unit output is higher and the efficiency of whichconversion from electricity to beam is lower.

Furthermore, with the laser decontamination device according to thepresent invention, it enhances the performance with which the RIs aredecontaminated further than the conventional counterparts and doeswithout any sections thereof being made into direct contact with thecontaminated article as in the case of such counterparts, so that itsolves the prior problems with the secondary contamination and theoperators being exposed to radioactive substances as well as in theaspect of cost reduction, it does without exchanging the contaminateddevice itself or the parts thereof and disposing with the ion-exchangeresins, with the result that the decontamination cost can be reduced.Further, even when the components of the device such as containers orcases might be contaminated, they can be decontaminated by the deviceitself.

Accordingly, the present invention allows the removal performance of theRIs to be far further improved than the conventional laserdecontamination devices and provides the laser decontamination devicethat solves the prior problems with environmental pollution caused bythe wasted secondary contaminants produced by the decontaminationmethods other than the laser method and with the exorbitant costincurred for disposing with such wastes, so that the industrialapplicability thereof is very high.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing the laser decontamination deviceaccording to the first embodiment of the invention.

FIG. 2 is a schematic view to explain the optical system of the laserdecontamination device according to the first embodiment of theinvention.

FIG. 3 is an explanatory view to show the effect brought into metals bythe laser decontamination device according to the invention.

FIG. 4 is an explanatory view to show the effect brought into concreteand ceramics by the laser decontamination device according to theinvention.

FIG. 5 is a view to explain the transversal pulse according to the highvelocity scanning by the laser decontamination device according to thepresent invention and the longitudinal pulse according to theconventional timing pulse device.

DESCRIPTION OF EMBODIMENTS First Embodiment

The first embodiment of the invention is explained with reference toFIGS. 1 to 4, in which the laser oscillator 1, the scanning device 2,the surface shape measuring device 3, the gas jet-spraying device 4 andthe removals collecting device 5 are illustrated.

(Arrangement of the Laser Decontamination Device)

According to the first embodiment, the laser oscillator 1 that is thelight source of a machining laser beam L₁ is connected through a longoptical fiber 11 to the scanning device 2 that condenses the laser beamL₁ onto the surface of a contaminated article T for scanning. To note,the fiber laser provided with the optical fiber 11 smaller in diameteris used for the laser oscillator 1.

Further, in the present embodiment, in order to further enhance thepower density of the laser beam L₁, not the pulse laser, but the CWlaser by which a focused beam size can be minimized is adopted for thelaser oscillator 1. Further, the CW laser costs lower than the pulselaser and its electricity to beam conversion efficiency is higher thanthe latter so that it is practically excellent in the cost-saving aspect(in the case of the pulse laser, the contaminated surface can be deeplypeeled off, but causes uneven decontamination density or some parts ofsuch surface to be remained without being decontaminated).

Further, as for the afore-mentioned scanning device 2, it comprises anXY axis scanner 21 to two-dimensionally and reflectively scan the laserbeam L₁ with beam reflectors 21 a and 21 a (galvano-mirrors) and a Zaxis scanner 22 to adjust the focal distance of the laser beam L₁ with amovable lens 22 a and a fixed lens 22 b comprising the condensing opticsystem, in which the laser beam L₁ passed through both the scanners isemitted onto the target from the laser window 23.

To note, the afore-mentioned Z axis scanner 22 is disposed nearer to thelight source (between the laser oscillator 1 and the XY scanner 21) thanthe XY axis scanner 21 and the laser beam L₁ scanned by the XY axisscanner 21 is irradiated onto the object without the intervention of anycompound lenses.

Furthermore, the scanning device 2 is provided with the surface shapemeasuring device 3 to measure the surface shape of the contaminatedarticle T. In this embodiment, the laser range finder 31 that irradiatesthe measuring laser beam L₂ onto the target and finds a distance fromthe phase difference by interference or the time difference between theirradiated light and the scattered light thereof is used for the surfaceshape measuring device 3 and is disposed such that the scanning of thelaser beam L₂ can be performed with the XY axis scanner 21.

Hereupon, the measuring laser beam L₂ of the laser range finder 31 isemitted from the laser window 23 through a mirror 32, a dichroic mirror33 (disposed on the optical path between the Z axis scanner 22 and theXY axis scanner 21) and the XY axis scanner 21. In turn, the scatteredlight is entered into the laser range finder 31 through the laser window23, the XY axis scanner 21, the dichroic mirror 33 and the mirror 32.

To note, the measuring laser beam L₂ of the laser range finder 31 can bescanned simultaneously with the machining laser beam L₁ with the XY axisscanner 21 for the purposes of performing the real-time shapemeasurement and machining, and the measuring laser beam L₂ may bescanned independently before the machining laser beam L₁ is scanned.Further, the shape data obtained at the laser range finder 31 are sentto the scamming device 2 through a data transmission means 34.

Then, irrespectively of whether or not the real-time shape measurementand machining is performed, the Z axis scanner is provided with thefocus position controlling section 24 to automatically adjust a focusposition according to an irradiation position such that the focus of thelaser beam L₁ comes on the surface of the contaminated article T basedon the shape data obtained at the surface shape measuring device 3,thereby, allowing the laser beam L₁ to be three-dimensionally scannedover and irradiated onto the surface of the contaminated article T.

Likewise, in the present embodiment, the focus position controllingsection 24 is set such that the surface of the contaminated article T tobe irradiated is adjustively placed within the range of the depth offocus (Rayleigh length) of the laser beam L₁ or in the vicinity thereof,but the focus spot can be freely adjusted by modifying the setting ofthe focus position controlling section 24 where necessary.

Then, as mentioned above, the advantage that the focus position of thelaser beam L₁ on the surface of the contaminated article T can beprecisely adjusted permits the power density of the laser beam L₁ to beenhanced further than before, with the result that even when the RIsmight invade into the contaminated article T through its cracks, asshown in FIG. 3, they can be momentarily spalled, evaporated andsublimated along with the base material by the laser beam L₁.

Elaborating further on the mechanism by which the contaminant is spalledby the laser beam L₁, in the heated surface of the contaminated articleirradiated by the laser beam L₁, microscopic cracks and defects existingin the inner layer of such surface start developing as shown in FIG. 4(a) and further develop as shown in FIG. 4 (b). Such inner layer issubjected to large compressing stress from the surroundingnon-irradiated sections as shown in FIG. 4 (c) so as to be finallybuckling out and jumping out the matrix and base material. To note, thedegree to which and the detailed process by which the contaminatedarticle is spalled, evaporated and sublimed differ according tomaterials to be irradiated.

Moreover, in the present embodiment, as with the scanning velocity ofthe scanning device 2, it is set at 10 m/s or higher and as shown inFIG. 5 (a), the scanning velocity and the focused beam size of the XYaxis scanner 21 are set such that a minute focused beam spot of themachining laser beam L₁ reciprocally running in the scanning directionis irradiated onto an arbitrary irradiation spot P on the irradiatedsurface during the duration of nanoseconds.

The above allows the decontamination device to cost lower and to berendered higher in output power than the conventional pulse laserirradiation type as shown in FIG. 5 (b) (e.g., as disclosed in JapanesePatent Unexamined Application No. 2007-315995) as well as non-thermalmachining free from uneven irradiation density to be feasible. To note,the afore-mentioned high velocity laser machining is realized by the XYaxis scanner 21 and the Z axis scanner 22 that scan the laser beam L₁with a small-sized optical member rotated with high velocity or movedwith a driving motor.

Furthermore, in the present embodiment, the output of the CW laser andthe Z axis scanner 22 are designed such that the power density is higherby three orders of magnitudes than that of the conventional counterpart(more concretely speaking, set at 1 GW/cm² or higher), so that most ofthe materials including stainless steel can be subjected todecontamination.

On the other hand, in this embodiment, the laser device is provided withthe gas jet-spraying device 4 to spray an inert gas from the outlet 41to the angular direction substantially contrary to the scanningdirection of the laser beam L₁ onto the surface of the contaminatedarticle T onto which the machining laser beam L₁ is being irradiated,which device 4 allows the irradiated surface of the contaminated articleto be constantly covered with an inert gas and the spalled, evaporatedand sublimed particles to be blown off.

Further, as for the removals blown off by the gas jet-spraying device 4,at the removals collecting device 5, those suctioned from the suctionport 51 are collected into the dusts collector 53 with a filter bagthrough the dusts separation catcher 52 (water-sealed metallic net). Tonote, the spalled, evaporated and sublimed particles of the contaminantscontaining the RIs as a whole are caught by the water-sealed metallicnet on the way, so that even the slightest secondary contamination canbe prevented.

Further, the scanning device 2 may well be mounted onto the arm sectionA of the remote-controlled robot R provided with the self-running means,thereby, controlling the robot R in a place away from it allowing theoperators to perform the decontamination without being exposed to theradioactive substances. To note, adjusting the length of the opticalfiber of the fiber laser permits the laser oscillator 1 to be disposedin a distant chamber or to be carried on the robot R.

Moreover, three-dimensionally controlling the arm section A permits thescanning device 2 to be driven at an arbitrary position on the surfaceof the contaminated article T, with the result that when a large wallsurface and as such is decontaminated, controlling the arm section Awith the position of the robot R fixed allows the decontamination to beefficiently performed.

The present invention is arranged substantially as described above,which is not limited to the above illustrated embodiment, but may bemodified into various manners within the scope of the accompanyingpatent claims. For instance, for the laser oscillator 1, not only thefiber laser, but also a semiconductor laser, a solid-state laser or agas laser capable of a high velocity scanning of 10 m/s and of such ahigh output power that the beam can be focused onto a minute area having10 μm or smaller in diameter so as to reach the power density of 1GW/cm² or higher (or lasers having the similar performance to BeamParameter Product 0.3 mmmrad in the same level as the single mode fiberlaser) may well be adopted.

Also as for the scanning device 2, the beam reflectors 21 a(galvano-mirrors) of the XY axis scanner 21 may well be altered with ahigh-velocity electro-optical device or resonant mirror and as such.Further, the movable lens 22 a of the Z axis scanner 22 may well bealtered with a variable focus lens, which lens (comprising a liquid orcrystal device) is electrically controlled so as to adjust a focaldistance with high velocity.

Moreover, as with the surface shape measuring device 3 as well, it doesnot necessarily use the laser range finder 31, which may be replacedwith other optical means (such as means for measuring the surface shapeof the target with triangulation or images other than the phasedifference in use, which means is capable of using minute optical pathshaving a diameter in millimeter or smaller over the whole optical path).

In turn, as for the removals collecting device 5, the other dustsseparation catchers 52 on behalf of the water-sealed metallic net maywell be used for catching the particles contaminated by the RIs.Further, the laser decontamination device itself may well be formed intoa portable size or a large-installation size, any of which modificationsalso belong to the technical scope of the invention.

INDUSTRIAL APPLICABILITY

Owing to the recent meltdown of the nuclear reactors here, thegovernment is scheduled to reinstate some of the damaged reactors or todecommission a number of the aged ones. It is prospected that the numberof the reactors to be decommissioned in the future might increase sothat it is hoped that various outstanding issues of the conventionaldecontamination methods (such as the operators being exposed toradioactive substances; recontamination caused by the contaminantscontaining the RIs; secondary wastes; exorbitant decontamination relatedcost; operational efficiency) be solved as soon as possible.

Under such circumstances, the laser decontamination device according tothe invention is excellent in the basic function of removing the RIsfrom the contaminated articles on almost all of the materials such ascarbon steel, stainless steel, titanium, aluminum, zirconium, tiles,concrete, zinc, glass, synthetic resins, coated films in comparison withthe conventional counterparts; generates no repulsive force; costslower; weighs lighter; is more readily feasible for automation; andfurther mitigates radiation exposure in comparison therewith, so thatits industrial applicability is considered very high.

NOMENCLATURE

-   1 laser oscillator-   11 optical fiber-   2 Scanning device-   21 XY axis scanner-   21 a Beam reflector-   22 Z axis scanner-   22 a movable lens-   22 b Fixed lens-   23 Laser window-   24 Focus position controlling section-   3 Surface shape measuring device-   31 Laser range finder-   32 Mirror-   33 Dichroic mirror-   34 Data transmission means-   4 Gas jet-spraying device-   41 Outlet-   5 Removals collecting device-   51 Suction port-   52 Dusts separation catcher (water-sealed metallic net)-   53 Dusts collector (with a filter bag)-   T Contaminated Article-   L₁ Machining laser beam-   L₂ Measuring laser beam-   R Remote-controlled robot-   A Arm section-   P Irradiation spot

1. A laser decontamination device comprising: a CW laser oscillator usedfor a light source of a machining laser beam; a scanning device providedwith an XY axis scanner to reflectively and planarly scan the laser beamwith beam reflectors and a Z axis scanner to adjust a focal distance ofthe laser beam with one of a variable focus lens and a movable lens,which Z axis scanner is disposed nearer to the light source than the XYaxis scanner and which scanning device condenses the laser beam scannedby the XY axis scanner and the Z axis scanner on a surface of acontaminated article without intervention of any compound lensintegrated with a plurality of lenses between the XY axis scanner andthe contaminated article; and a surface shape measuring device tomeasure a surface shape of the contaminated article by an optical meanscomprising a laser range finder and the XY axis scanner, wherein the Zaxis scanner of the scanning device is provided with a focus positioncontrolling section to automatically adjust a focus position accordingto an irradiation position such that a focus of the laser beam comes onthe surface of the contaminated article based on a shape data obtainedat the surface shape measuring device, thereby, allowing the laser beamto be three-dimensionally scanned over and irradiated onto the surfaceof the contaminated article with the focus spot aligned in pinpointingwith the surface of the contaminated article.
 2. The laserdecontamination device according to claim 1 wherein a single mode fiberlaser whose average output power is large and that allows the beam to befocused on a minute spot having 10 μm or smaller in diameter is adoptedfor the laser oscillator, wherein an output of the laser oscillator isadjusted and an optical system is designed such that the laser beam canbe irradiated onto a surface of the contaminated article at a powerdensity of 1 GW/cm² or higher in a halt condition.
 3. The laserdecontamination device according to claim 1 wherein a scanning velocityof the XY axis scanner is set at 10 m/s or higher as well as thescanning velocity and a focused beam size of the XY axis scanner and afocused beam size are set such that the reciprocally scanned machininglaser beam is irradiated onto a arbitrary minute spot on an irradiatedsurface during duration of nanoseconds.
 4. The laser decontaminationdevice according to claim 1 wherein the focus position controllingsection is set such that the surface of the contaminated article to beirradiated is adjustively placed within a range of a depth of focus(Rayleigh length) of the laser beam or in a vicinity thereof.
 5. Thelaser decontamination device according to claim 1 wherein for thesurface shape measuring device, a laser range finder that irradiates ameasuring laser beam onto a target and finds a distance from one of aphase difference by interference and a time difference between anirradiated light and its scattered light is adopted, which finder isdisposed directly in front of the XY axis scanner such that themeasuring laser beam can be scanned simultaneously with or independentlyfrom the machining laser beam with the XY axis scanner.
 6. The laserdecontamination device according to claim 1 wherein the laser oscillatoris disposed away from the scanning device and a fiber laser having anoptical fiber smaller in diameter is adopted for the laser oscillator,wherein the Z axis scanner, a dichroic mirror and the XY axis scannerare disposed in this order between an emitting end of the optical fiberand a laser window.
 7. The laser decontamination device according toclaim 1 further comprising a gas jet-spraying device to blow offparticles with an inert gas jet-sprayed in an angular directionsubstantially contrary to the scanning direction of the laser beam ontothe surface of the contaminated article onto which the machining laserbeam is being irradiated and the irradiated surface constantly coveredwith the inert gas; and a removals collecting device to suction and tocollect removals containing radioactive substances blown off by the gasjet-spraying device
 8. The laser decontamination device according toclaim 1 wherein the laser oscillator is carried on a remote-controlledrobot provided with a self-running means and the scanning device ismounted onto an arm section of the remote-controlled robot so as to makethe scanning device drivable in a wider area of the surface of thecontaminated article.